Audio signal amplifier



FIG. 1 is a perspective view of the top, front and right side of an audio signal amplifier showing my new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a front elevational view thereof; and,

FIG. 4 is a bottom plan view thereof.

The dot-dash-dot broken lines represent the boundary of the claim. The evenly spaced broken lines show portions of an audio signal amplifier that form no part of the claimed design. 

The ornamental design for an audio signal amplifier, as shown and described. 